Powder cloud generating apparatus



May 3, 1960 c. L. HUBER POWDER CLOUD GENERATING APPARATUS 2 Sheets-Sheet1 Filed May 26, 1958 DEVELOPMENT ZONE AEROSOL HANDLJNG POWDER CLOUDGENERATOR REGULATING VALVE COMPRESSOR F/GZ INVENTOR. Charles L. Huber IATTORNEY y 1960 c. L. HUBER 2,935,234

POWDER CLOUD GENERATING APPARATUS Filed May 26, 1958 2 Sheets-Sheet 2 666; 3 67 V f 1 WHIHHIIII l H 254/ A FTTI [[V l t f 1 I 42 49 46 45 a5 40k 8 26 1%: 39 37 20 a! 6 A n 32 a 29 3/ 2/ n u 1/ 7/ 26 f 27 77 I 25 i iI 1!! INVENTOR.

Charles L. Huber BYWVK/ZZA/ A T TORNE V United States Patent F POWDERCLOUD GENERATING APPARATUS Charles L. Huber, Byron, N.Y., assignor toHaloid Xerox Ind, Rochester, N.Y., a corporation of New York ApplicationMay 26, 1958, Serial No. 737,584

5 Claims. (Cl. 222-193) This invention relates to the field ofxerography and, particularly, to an improved powder cloud generatormetering apparatus for powder cloud development of xerographicallyproduced images. More specifically, the invention relates toimprovements in powder cloud generators of the type disclosed incopending Hayford et a1. application Serial No. 489,257, filed February18, 1955, now Patent No. 2,862,646, issued December 2, 1958, and incopending Hayford et a1. application Serial No. 737,- 939, filedconcurrently herewith on May 26, 1958.

In the process of Xerography, for example, as disclosed in CarlsonPatent 2,297,691, issued October 6, 1942, a xerographic plate comprisinga layer of photoconductive insulating material on a conductive backingis given a uniform electric charge over its surface and is then we posedto the subject matter to be reproduced, usually by conventionalprojection techniques. This exposure discharges the plate areas inaccordance with the light intensity that reaches them, and therebycreates an electrostatic latent image on or in the photoconductivelayer. Development of the latent image is effected with anelectrostatically charged, finely divided material, such as anelectroscopic powder, which is brought into surface contact with thephotoconductive layer and is held thereon electrostatically in a patterncorresponding to the electrostatic latent image. Thereafter, thedeveloped xerographic powder image is usually transferred to a supportsurface to which it may be fixed by any suitable means.

Two methods of image development are in common use. One is described inWalkup U.S. Patent 2,618,551 and is known as cascade development, and isin general use for line copy development. In this technique, the powderis mixed with a granular material, and this twocomponent developer ispoured or cascaded over the plate surface. The function of the granularmaterial is to improve the flow characteristics of the powder and toproduce, on the powder, by triboelectrification, the proper electricalcharge so that the powder will be attracted to the image. More exactly,the function of the granular material is to provide the mechanicalcontrol to the powder, or to carry the powder to an image surface and,simultaneously, to provide almost complete homogeneity of chargepolarity. The other form of development is known as powder clouddevelopment, and is in general use for continuous tone development. Inthis technique of development, a dispersion of electrically chargedpowder particles in an aeriform fluid is passed to the surface bearingthe electrical image and particles are drawn from the aeriform fluiddispersion to form a powder image on the plate. This form of developmentis disclosed and described in Carlson U.S. Patent 2,221,776 wherein arotating vane wheel or propeller is used to stir up powder in a chamber,thereby creating a cloud of particles for presentation to theelectrostatic image. The vane or propeller in that patent may beconnected to a terminal of a battery to impart charge to the powderparticles.

Generally in powder cloud creating apparatus there is included a powdersource, means to create a cloud of 2,935,234 Patented May 3, 1960 powderin aeriform fluid, means to convey the cloud to a surface carrying anelectrostatic image, and means to electrostically charge the powder inthe cloud before it reaches the surface. Such devices, which include oneor a number of the above elements, and which are used to take powderfrom a source whether it be a mound of powder or whether it be in othershapes or forms and convert the powder to an aerosol of powder inaeriform fluid is herein, and generally in the art, referred to as apowder cloud generator or as a cloud generator, as described in HayfordU.S. Patent 2,812,883 and in the above referred to copending Hayford eta1. application, Serial No. 489,257.

An object in the art of xerography, as in any art concerned with imagereproduction, is that of uniformly developing high quality copy. Meansof obtaining this objective, while using powder cloud development, isthrough the uniform and constant presentation to the electrostaticlatent image on a surface of a powder cloud of fine developer powderparticles uniformly and densely dispersed throughout.

This invention is concerned with uniformly loading a powder support anduniformly dispensing the powder particles loaded onto the support in theform of a powder cloud. The support of this invention is capable ofdelivering uniform dispersions of great quantities of powder in anaeriform fluid. Further, the device of this invention is able to operateover long periods of time and can produce continuous outputs which aresufficient for rapid processing in Xerography.

The support is enclosed in a housing and rotated or moved in asubstantially horizontal plane. At one point on the surface of thesupport is positioned raw or bulk developer powder particles. Theseparticles are held in position by a first scraper or meter blade, whichalso acts to meter out a layer of powder to the surface of the supportas it moves or rotates beneath the powder supply and first scraper. Afirst brush then flufis up the powder which is then again metered by asecond scraper, excess powder being returned to the pile in front of thefirst scraper. The particular surface of the support, described indetail hereinafter, is one which loads uniformly as it passes beneaththe powder supply. An aeriform fluid is flowed into the housing at onepoint and powder in the aeriform fluid flows out of an output tube. Anoutput orifice is connected within the housing to the output tube and ispositioned at a distance above the surface of the support. Particles onthe surface of the support are entrained in the flow of the aeriformfluid traveling from the housing out the output orifice and through theoutput tube, thereby creating at the output end of the output tube anaerosol of powder particles.

It is, therefore, the object of this invention to improve upon powdercloud generators so that a uniform and dense dispersion of powderparticles in an aeriform fluid is created.

A further object of this invention is to provide a new powder cloudgenerator in which powder is uniformly loaded to a surface and thenentrained in the flow of an aeriform fluid out an output tube.

For a better understanding of this invention, together with otherfurther objects thereof, reference is now had to the followingdescription taken in connection with the accompanying drawings, and thescope of the invention will be pointed out in the appended claims.

Fig. l is a block diagram of elements which would generally appear inxerographic cloud creating apparatus for use in developing electrostaticimages.

Fig. 2 is a top view of the powder cloud generator with parts brokenaway to show the internal structural elements of the device.

' 3 Fig. 3 is a cross-sectional view of the powder cloud generator takenalong line 33 of Fig. 2, and

Fig. 4 is a detail sectional view of the mounting means for the meterblades taken along line 44 of Fig. 2.

eferring now with more particularity to the drawings, in Fig. l is showna block diagram of elements which compose cloud creating apparatus fordevelopment of electrostatic images. As is indicated in this diagram,compressed aeriform fluid is fed from compressor 11 to a powder cloudgenerator 13 through a regulating valve 12 and the output of the powdercloud generator is fed through aerosol handling means 15 and then to thedevelopment Zone 16 whereat developer particles are passed fordevelopment purposes to a surface carrying an electrostatic latentimage.

The source of compressed or pressurized aeriform fluid may be anysuitable source, such as, for example an air pump or like'pressuregenerating member or a suitable pressurizedgas container. Suchcontainers are readily available on thecornmercial market in the form ofgas capsules of'carbon dioxide or the like under pressure, in the formof bombs or the like of gas such as fluoro chloroalkanes, which areavailable under the general family name of Freon. Similarly, a suitablesystem may comprise a pump or generating means optionally in combinationwith a pressure chamber whereby fluctu ations in pressure may be limitedor avoided.

Regulating valve 12 is used to control the rate of flow of aeriformfluid from compressor 11 to powder cloud generator 13 and also tocontrol the pressure of gas supplied to the powder cloud generator. Thepowder cloud generator, which is the next block in this diagramfollowing regulating valve 12, is used to create an aerosol of powder inair. It may be supplied with powder in what may be termed the raw orbulk form, that is, powder taken directly from a container and directlysupplied in that form without treatment. with powder which is firsttreated and then placed in position in the generator. The particularpowder used is dependent on a number of factors such as other elementsused in the cloud creating apparatus, the form of xerographicdevelopment, the desired quality of final copy,.,and the like. A moredetailed discussion of powders will appear below.

'The aerosol handling block 15 of the diagram appearing in Fig. 1 mayrepresent any number of means and apparatus for imparting anelectrostatic charge or deagglomerating. the individual powder particlesin the I aerosol supplied from the powder cloud generator. Charging anddeagglomeration of particles may be accomplished by turbulently flowingthem through fine capillary tubes, such as disclosed in copending Rickerapplication Serial No. 353,520, filed May 7, 1953. Charging may beaccomplished by passing the aerosol of powder in air through a coronadischarge zone, or the like. r

The aerosol composed of charged particles in gas is next supplied, asindicated by the block diagram, to development zone 16. Generally, thiszone includes a means for expanding the aerosol to a cloud, andoptionally this may be done by leading the air from tubes or the like toa larger area where the aerosol expands, creating the cloud of chargeddeveloper particles in gas. It is also feasible and sometimes desirableto use the particles in aerosol form without expansion.

In xerography in order to develop a true copy of the original image, itis generally desirable to develop against gravitational pull in that theelectrostatic charges on the plate surface truly represent the patternof the image projected to the plate surface, and allowing gravitationalforces to operate in causing deposition of powder particles may resultin a distorted reproduction. Also in causing the particles to depositagainst the pull of gravity, deposition on the image bearing surface ofagglomerates is reduced. This may be accomplished by positioningtheplate It may also be supplied aoaaasa with the-image bearing surfacefacing downward and creating a cloud beneath it. In some instancesparticles deposited because of other forces may be removed during thedevelopment process through the use of such techniques as directingslight air currents or winds to the plate surface. Such winds orcurrents should be sufiicient to remove particles not held in place dueto electrostatic forces, but should be limited so that particleselectrostatically held in place are not affected.

Reference is now had to Figs. 2 to 4, inclusive, wherein is shown apreferred embodiment of a powder cloud generator 13 according to thisinvention. The flanged, cupshaped body or casing 20 has mounting lugs 21formed integrally therewith for supporting the unit on a structuralelement (not shown) of the xerographic machine and an air inlet'opening55 for connection to a source of aeriform fluid under pressure' Theshaft 22, which may be driven by any suitable power means (not shown),is journaled in double sealed bearings 23 and 24 mounted in the hub 25of the body or casing 20. A groove 26 extends along the bored wall ofthe hub 25 to permit equalization of pressure on both sides of thebearing 23, while thebore opening in the hub 25 is sealed by oil seals27 positioned between the bearings 23 and 24.

A cup-shaped powder carrier element 28- is rotatably positioned in thecasing 20 and is secured against a shoulder of. the shaft 22 by means ofthe washer 29 and a screw fastener 30. The powder carrier element 28consists of a backing rigid plate31, the upper surface of which is facedwith a skin or support 32 having numerous interstices in the surfacethereof for carrying powder particles, suitable materials, such ascotton flannel, for the skin or support 32 being more fully described inabove referred to copending Hayford et al. application Serial No.489,257. A shell 33 is fastened by screws 34 to backing plate 31 toretain powder on the backing plate.

First and second meter blades or scrapers 35 and 36, respectively, areadjustably positioned over the skin or support 32 in the powder carrierelement 28, for metering powder across the surface of the powder carrierelement 28, and first and second brushes 37 and 38, respectively, arespring mounted against the surface of the skin or support 32 to agitatepowder particles deposited on the surface thereof. To accomplish this,bearing blocks 39, which rota-tably carry adjustment screws 40positioned by retaining rings 41 are fastened as by soldering to meterblade 35. Internally threaded blocks 42 and 43 are secured by solderingto the plate 44, the block 42 also supporting on a shoulder thereof abrush carrier 45 to which brush 37 is rotatably secured. The meter blade35 is secured to the plate 44 by threading the adjustment screws 40 intothe blocks 42 and 43. v

The assembly of the meter blade 36 to the plate 44 is similar to theassembly of meter blade 35 to the plate 44, except that the brushcarrier 46 is supported by block 42, the brush carrier 46 rotatablysupporting brush 38. By'

means 'of the adjustment screws '40, the meter blades 35 and 36 can beadjustably positioned relative to the surface of the skin or support32,, and the position can be maintained by locking the adjustment screws40 against further movement by nuts 47.

The plate 44, carrying the meter blades 35' and 36' and the brushes 37and 38, is fastened by machine screw 49 and lockwasher 50, to yoke 48secured byfasteners 53 to the shoulder 51 formed in the flange 52 of thebody or casing 20. Apertures 54 in the yoke 48 permit access from thetop'to'the nuts 47 and adjustment screws 40.

Theopen end of the casing or body 20 is closed by the cover plate 60held in position by lockwashers 61, and

bolts- 62, and sealed by O-rings gasket 64 held in an annular recess inthe upper face of the flange 52. The cover plate 60 secured to the bodyor casing 20 forms a housingJgenerally designated 77, which surroundsand en compasses the internal elements: The cover plate 60 is providedwithanopening 65'located. so that powder ma terial may be supplied tothe powder carrier element 28 in front of the meter blade 35. A closureplate 66 for the opening 65 seats at its periphery on a gasket 67 heldin an annular recess in the upper surface of the cover plate 60, and issecured by lockwashers 61 and bolts 62 and 63.

The cover plate 60 is also provided with a threaded opening 68 receivingan externally threaded hollow cylinder 70 adjustably secured by lockingnut 71 and sealed by gaskets 72 and 73 held in annular recesses in thelocking nut 71 and cover plate 60, respectively. A bored output tube 74adapted to be secured to a discharge conduit (not shown) is fastened inthe upper portion of the hollow cylinder 70, while a pick-up tube 75, inwhich a relatively large number of output orifices 76 are formed, issecured in the bottom portion of the hollow cylinder 70.

As has been previously pointed out, an object of this invention is tometer controlled amounts of developer powder particles to a surface andto pass this powder from the surface in an aerosol of powder in air tocreate a uniformly dense and constant powder cloud output. To accomplishthis, a reserve or supply of developer powder is placed on the skin orsupport 32 of the powder carrier element 28 through the opening 65 andafter the closure plate 66 is secured, air inlet opening 55 is connectedto a source of high pressure air. The surface of the skin or support 32is one that tends to draw powder with it and thereby becomes coated withpowder when it moves beneath the powder supply or powder reserve. As thepowder carrier element 28 is rotated by means of shaft 22, a smallquantity of powder carried by the support is permitted to pass under themeter blade 35 while the remainder of the supply of powder is retainedagainst the face of the meter blade.

Generally the meter blade or scraper 35 is curved to best retain powder;that is, it is desirable to form this blade to avoid movement of powderpast the edges of the blade. It is also desirable to form the bladecurved in shape so that the larger mass of powder congregates at thatarea over the flat surface of the powder carrier element 28, which willpass under output orifices 76 where powder will be removed. Whether themeter blade or scraper 35 is curved, as shown, or straight, the portionof the meter blade positioned over the annular surface portion of powdercarrier element 28 which passes under the center of pick-up tube 75should be tangent to a radius of the powder carrier element 28 so thatthe powder carried on the above described annular surface portion willstrike the blade at right angles causing powder to remain positionedadjacent to the blade over this annular surface portion of the powdercarrier element. The lower edge of retaining scraper or meter blade 35,which is similar to the lower edge of meter blade 36, is preferablystraight, that is, it is not indented, and it is preferably spaced apartfrom the flat bottom surface of powder carrier element 28.

. Allowing too little powder to pass beneath the meter blade creates toothin an aerosol of powder particles, whereas allowing too much powder topass under the meter blade will create too dense an aerosol of powderparticles. Denseness is a desirable feature of an aerosol; yet, when anaerosol of powder in gas is too dense, fine grain development isdetrimentally affected in that the aerosol tends to be a presentation ofbulk powder including agglomerated powder to the output zone rather thana compressed cloud of powder particles in gas. The density of powder ingas or of the aerosol is a factor Which relates to the particular usethe aerosol is to be put to. For example, in the development of linecopy of normal printed pages, it is quite proper and not unpleasing tothe eye to develop with larger sized particles or particles of smallersizes which are less deagglomerated than in the case of the developmentof continuous tone images wherein it is desirable to develop withdeagglomerated and individual particles and smaller sized particles. Inline copy work, then, the meter blades or scrapers may beadjusted toallow passage of a greater quantity of particles to the surface beingloaded, whereas when developing fine grain continuous tones, it isdesirable to pass a lesser quantity of powder particles beneath themeter blades or scrapers. Spacing of the meter blades or scrapers fromthe surface being loaded relates to the particular surface material andto the particular powder particles being used. Adjustment of both meterblades 35 and 36 with respect to the membrane 32 is done by means of theadjustment screws 40 and nuts 47.

It has been found that, for a fixed setting of the meter blade 35 withrespect to the skin or support 32, the amount of powder metered by theblade will vary. To obtain satisfactory coverage of powder particlesover the surface of the covering or membrane 32, a relatively largesupply of powder must be retained in front of the meter blade 35. As thesupport passes under the supply of powder, the powder particles willpack tightly and clog the interstices of the support. Clogging willdepend generally on the particular powder being used, the amount ofpowder, and the particular material of the support. Clogging presents areal problem, in that once an area becomes clogged with powder, ineffect the powder becomes a portion of that particular part of thesupport, and when that area is presented to the powder supply forreplenishment, it will pick up less powder than an area which is notclogged. Packing will depend on the quantity of powder retained in frontof meter blade 35, the quantity varying as the device is operated.

To obtain fine control of the powder metered, the brush 37, mounted nextin line to the meter blade 35 in the direction of rotation of the powdercarrier element, agitates the powder sufliciently to fluff up the powderparticles and thereby prevent caking and also provides a load of uniformtexture in front of meter blade 36. The loosely packed powder is thenre-metered by meter blade 36. If a relatively large supply of powder ispermitted to build up in front of meter blade 36, the efiiciency of thisblade will decrease. To prevent a build-up of powder in front of meterblade 36, the blade is mounted so that powder removed by this blade isreturned to the powder supply in front of meter blade 35. This isaccomplished by mounting the meter blade 36, whether a straight blade orcurved, as shown, so that the angle of incidence A, of the moving powderparticles striking the blade, is an acute angle as indicated in Fig. 2.The angle of incidence A is defined as the angle formed by the line Ttangent to the path of movement of a powder particle on the surface ofpowder carrier element 26 as it is rotated, and a line N perpendicular(normal) to the meter blade 36 at the point M of incidence of the movingpowder particle on the meter blade 36. the blade, is composed of avector force normal to the blade and a vector force tangent to theblade. The latter force will cause the excess powder particles, removedby the meter blade 36, to pass off the inner edge of the blade fromwhere it will be returned by movement of the powder carrier element 28to the front of the meter blade 35. Whether the meter blade or scraper36 is curved, as shown, or straight, the meter blade or scraper must bepositioned at an angle to the radius of the powder carrier element 28,and specifically in regard to a curved blade, it is preferred that noportion of the blade facing meter blade 35 should be tangent to a radiusof the powder carrier element so that all powder particles striking thisblade strike it at an angle other than normal. In this respect it isnoted that the powder carrier element is rotated at a low speed so thatthe centrifugal force acting on the powder particles is insignificant.

Thus it is apparent that meter blade 36 must be positioned to performtwo functions, that is, the meter blade 36 must be positioned behind thefirst meter blade 35 to meter the desired amount of powder particles tothe an- The resultant force, which is at an angle to p 7 nular surfaceportion of powder carrier element 28 which passes directly under pick-uptube 75, and. the meter blade 36 must be positioned so that all excesspowder particles. are projected onto a second annular portion of powdercarrier element 28 to be returned to the powder supply in front of meterblade 35. If the meterv blade 36 is not positioned to perform thislatter function, the excess powder particles would pile up in front ofthis blade to the extent that after a short period of operation theentire powder particle supply would be retained by meter blade 36 inlieu of meter blade 35. If this is permitted to occur, meter blade 36 ineffect becomes the sole meter-. ing blade in the system since it wouldthen perform the same function as meter blade 35, while meter-blade35would become useless. It is apparent then, that, in an apparatusconstructed in accordance with the instant -in-- vention, meter blade 36is nota mere duplication of meter blade 35, since each meter differentfunctions. a

However, it is brush 37, placed between; meter blades 35 and 36, thatpermits very fine control of the amount of powder metered. With arelatively large'supply of powder particles retained in front of meterblade 35, the layer of powder particles adjacent to covering 32 will bemore tightly packed than when the supply of powderis nearly exhaustedand, therefore, during the operation of the device the actual quantityof powder advanced to meter blade 36 will vary because of the variationin density of the layer of powder particles. Brush 37 fluffs up thislayer of powder particles so that a uniform textured layer of powderparticles is presented to meter blade 36. Thus it is apparent that whilemeter blade 35', for example, will scrape ofi powder from a pile ofpowder varying in height from say three inches down to a quar- 7 ter ofan inch with corresponding variations in density throughout the pile,the layer of powder reaching meter blade 36 will vary in height by onlya few thousandths of an inch, since the powder particles have beenpreviously partially metered by meter blade 35 and then fluffed up bybrush 37 to provide a uniform textured layer of powder particles.

-The brush 38 causes agitation ofpowd'er particles deblad'e must perform7 posited on the covering 32 which have passed by meter 7 carriers and46, respectively, so that a slight tension exists between the brushfibers and the surface of the skin or support 32 causing the brushes torotate as a result of the movement of the powder carrier element 28.Rotation of the brushes 37 and 38 causes the brush bristles to rotateagainst and flick away powder particles from the surface of the support.The brush 38 should be so positioned and should be of such'size so as tostir up any powder particles on that portion of the covering whichpasses beneath the output orifices 76. The layer of metered powder onthe covering is then picked up by the output orifices and dischargedthrough the outlet plug 7 4.

The pick-up tube 75 is positioned in the casing so that the openings ofthe output orifices are adjacent but spaced an appreciable distance fromthe surface of the skin or support 32. With this arrangement there 'isestablished a zone of pressure, between the output orifices and the suchas the particular surface material being loaded, the

particular developer powders'being used, the gas flow and gas pressuresupplied to the device, the use desired 7 of the output, and the like.For a generator constructed 15 along lines of the embodiment shown inFigs; 2 and 3, it has been found that revolving the powder carrierelement at a rate of 1 to 5 revolutions per minute and preferably at 3revolutions per minute tends to give optimum outputs. It is to beunderstood, of course, that the output of powder in gas tends toincrease as the revolutions per minute of the powder carrier elementincreases. If it is, therefore, desired to continue receiving a densecloud with more gas pressures and lower gas flows, a dense cloud may beobtained with more revolutions per minute.

The principle of operation of the powder cloud generators beingdescribed herein is one of flowing gas into an enclosure having anoutput tube. Since the output tube is the only exit for the gas flow,the gas being flowed into the device leaves through the output tube. Theoutput orifice attached to the output tube is closely spaced to theloaded surface and the gas rushing out the output orifice entrains intoits stream 'the powder particles carried by the loaded surfacepositioned beneath or substantially beneath the output orifice. Theoperation of the device when operating properly removes completely allloaded powder from the loaded surface. As an aid to the completeremoval, the brush stirs up the powder particles so that they'may moreeasily become entrained in the gas flow rushing out the output orifice.

, Thus it is clear that increasing the speed of rotation of the ness ofcloud, in that all particles are entrained in lower.

gas flow rates and the same amount of particles for a larger flow of gaswill create a thinner aerosol of powder particles.

Certain features relating to the developer material are pertinent inoperating the powder cloud generator'and pertinent in developingelectrostatic images. In general, particles should be grossly smallerthan the output tube diameter, and it may be stated that finer sizedparticles in the absence of undue agglomeration may reveal a print orpicture more pleasing to the eve'than larger sized particles. Thus, aconvenient particle size which results in extremely high quality copycontemplates particles of sub-micron size having average diameters inthe order of 0.1 micron. From the point of view of composition of thedeveloper particles, prints or pictures may be produced with avariety'of types of finely divided electroscopic powders as disclosed inthe Carlson patent. However, as the art of xerography has progressed, ithas been found preferable to develop images with a powder formed of anyof a variety of pigmented thermoplastic resins that have beenspecifically developed for the purpose. A number of such developingmaterials are, manufactured and marketed by Haloid Xerox Inc., ofRochester, New York,

and are specifically compounded for producing dense images of highresolution and to have characteristics to permit convenient storage andhandling. 7

The amount of developer particles placed in front of meter blade orscraper 35 is dependent on the amount determines how much this meterblade'will retain.

Preferably, in a powder cloud generator, constructed in accordancewith'the invention, for use on a xerographic machine for producingcontinuous tone reproductions developed with sub-micron sized powderparticles, botlr meter blades 35and 36 are spaced .005" above a cottonflannel skin or covering 32 while pick-up tube is'spaced .100 above theskin or covering 32. Obviously, the spacing of meter blades 35 and 36and of the pick-up'tube 75 with respect to the skin or covering 32 maybe varied, for example, according to the size of the powder particlesused, the particular surface material being loaded, and the like.

While the present invention as to its objects and ad- 9 vantages, as hasbeen described herein, has been carried out in specific embodimentsthereof, it is not desired to be limited thereby, but is intended tocover the inven tion broadly within the spirit and scope of the appendedclaims.

What is claimed is:

l. A powder cloud generator including an enclosure having an inletopening for compressed fluid, an inlet means for powder material and anoutput means for the powder cloud; a powder carrier means, including asupport for powder particles, rotatably journaled and sealed in saidenclosure, metering means including first and second meter bladesconnected to said enclosure, said first and second meter blades beingpositioned in closely spaced relationship above said support, and saidsecond meter blade being further positioned so that the angle ofincidence of the powder particles carried by said support with saidsecond meter blade is an acute angle, whereby excess powder particlesare deflected to be returned by said support to said first meter blade,and a first brush and a second brush rotatably connected to saidenclosure and positioned in contact with said support, said first brushbeing located between said first meter blade and said second meterblade, and said second brush being located between said second meterblade and said output means, said output means including a pick-up tubein said enclosure and which has at least one output orifice adjacent tobut spaced from said support.

2. A powder cloud generator including an enclosure having an inletopening for compressed aeriform fluid, an inlet means for powdermaterial and an output means; a powder carrier means, including asupport, rotatably journaled in said enclosure, said support beingarranged to receive a supply of powder particles from said inlet means,metering means, including at least a first meter blade and a secondmeter blade, mounted in said enclosure so that said first meter bladeand said second meter blade are positioned a slight distance above saidsupport and said second meter blade is also positioned so that excesspowder deflected by said second meter blade is returned to said firstmeter blade, and a brush means mounted to said enclosure in contact withsaid support and positioned between said first meter blade and saidsecond meter blade in the direction of rotation of said support toagitate powder particles on said support.

3. A powder cloud generator including an enclosure having an inletopening for compressed aeriform fluid, an inlet means for powdermaterial and powder output means for a suspension of powder material inan aeriform fluid; powder support means rotatably mounted in theenclosure, said powder output means including at least one outletorifice positioned in closely spaced relation above said support means,and powder metering means secured to said enclosure and arranged in thepath of movement of said support means for determining the quantity ofpowder supplied to the output means, said last recited means comprisinga first metering blade arranged in the path of movement of said supportmeans and in spaced relation above said support means for limiting thesupply of powder on said support means passing therebeneath to an amountslightly in excess of that to be delivered to the output means, a brushmeans positioned next adjacent to said first metering blade and incontact with said support means, a second metering blade arrangedintermediate said first metering blade and said output means and in thepath of movement of said support means, said second metering blade beingpositioned in closely spaced relation above said support means to limitthe supply of powder on said support means passing therebeneath to anamount equal to that to be delivered to the output means, and beingpositioned at an angle relative to the path of movement of the powder todeflect excess powder from the output means.

4. A powder cloud generator including an enclosure having an inletopening for compressed aeriform fluid, an inlet means for powdermaterial and powder output means for a suspension of powder material inan aerifrom fluid; powder support means rotatably mounted in saidenclosure, said powder output means positioned in closely spacedrelation to said powder support means for withdrawing powder from theenclosure, and powder metering means connected to said enclosure andarranged in the path of movement of powder on said support means fordetermining the quantity of powder supplied to said output means, saidlast recited means comprising a first metering blade arranged in thepath of movement of said support means and in spaced relation to thesupport means for limiting the supply of powder to an amount slightly inexcess of that to be delivered to the output means,'a second meteringblade arranged intermediate the firstmetering blade and the output meansand in the path of movement of said support means, said second meteringblade being positioned in closely spaced relation to said support meansto limit the supply of powder to an amount equal to that to be deliveredto said powder output means, and being positioned relative to the pathof movement of the powder to deflect excess powder from the. outputmeans into a position on said powder supporting means to be metered bysaid first metering blade, and a first brush and a second brushrotatably positioned in contact with said support means, said firstbrush being located between said first metering blade and said secondmetering blade, and said second brush being located between said secondmetering blade and said powder output means.

5. A powder cloud generator including an enclosure having an inlet forcompressed aeriform fluid, an inlet means for powder material and anoutput means for a powder cloud; a powder carrier means, including acircular support for powder particles, rotatably journaled and sealed insaid enclosure, said output means including a pick-up tube having atleast one output orifice therein adjacent to but spaced from saidsupport, support means connected to said enclosure and positioned oversaid support, a first meter blade connected to said support means andpositioned in closely spaced relation above said support to retain asupply of powder particles on said support, a first brush rotatablyconnected to said support means between said first meter blade and saidpickup tube in the path of rotation of said powder carrier means, saidfirst brush contacting said support, a second meter blade connected tosaid support means and positioned in closely spaced relation above saidsupport between said first brush and said pick-up tube, said secondmeter blade being further positioned at an angle to the radius of saidpowder carrier means, and a second brush connected to said support meansin contact with said support and positioned between said second meterblade and said pick-up tube.

References Cited in the file of this patent UNITED STATES PATENTS2,213,508 Wheldon Sept. 3, 1940 FOREIGN PATENTS 833,320 Germany Mar. 6,1952

